Extrusion apparatus involving rotations

ABSTRACT

One or several strands of a material in plastic state are laid in pressure-free fashion into an exposed exteriorly accessible circular inlet channel of an extrusion die, while at least the diepart or dieparts, which define the inlet orifice are rotated so as to distribute each strand generally helically in the channel, and a driving shear force is applied against the material in the inlet channel to advance the material towards the die orifice, from where it is extruded in form of a tubular film or a circular array of filamentituous elements. The driving shear force can be established by rollers or scrapers engaging with the inlet orifice, or by moving the two sides of the inlet orifice relative to each other preferably in connection with an internal vanes adapted to produce a pumping action, or by an inserted ring in the orifice.

This is a division of Ser. No. 639,006, filed Dec. 9, 1975, now U.S.Pat. No. 4,115,502, issued Sept. 19, 1978.

BACKGROUND OF THE INVENTION

The present invention relates to the extrusion of a tubular item or acircular array of filamentituous items from any material formable byextrusion. Thus it covers the extrusion of a great variety of endproducts, such as e.g. tubular film, pipes, twine, rope material andtextile yarn from thermoplastic polymers, but also e.g. extrudedfoodstuff, glass and ceramic articles.

An object of the invention is to achieve improved circumferentialdistribution in the extrusion of tubular structures or circular arraysof filaments or the like, in particular in connection with materialswhich due to great deviation from Newtonian behaviour are difficult todistribute evenly over the circumference by conventional means, or inconnection with co-extrusion.

As known it is relatively easy to carry out an even coextrusion of e.g.4-5 layers in a flat die, because the spacing of each of the internalslots for the different materials can be adjusted at small intervals,but similar adjustment means do not exist for tubular co-extrusion.Therefore there is a great need for devising an improved distributionsystem in connection with circular coextrusion.

A second object of the present invention is to provide for a simplemethod and device for coextrusion of a relatively big number of layers.

A third object is to mechanically improve the bonding between layers ofdifferenct coextruded materials by forming fine ribformed mutuallyinterspersed extensions of the layers.

Other objects of the invention will appear from the followingdescription.

SUMMARY OF THE INVENTION

The present invention which as mentioned above relates to the extrusionof a tubular item or a circular array of filamentitous items from anymaterial formable by extrusion in plastic state, is characterized by thesteps of feeding (usually from a conventional extruder) at least onestrand of the material in plastic state into a circular inlet orifice ofan extrusion die, distributing the material evenly over thecircumference of the inlet orifice by rotation of the material aroundthe central axis of said circular orifice, creating a driving shearforce at said orifice, and hereby extruding the material to an exit partof the die while maintaining it in form of a tubular stream or acircular array of streams.

The rotation of the material in the inlet orifice will lay-up eachstrand in helical manner and will thereby produce an even distributionover the circumference. At the same time the die itself will work asmelt-fed extruder.

As it will appear more clearly from the drawings and the desciption ofthe latter, there is no need to establish a sealed-off connectionbetween the apparatus part from which the strand or strands are fed intothe inlet orifice and the rotating diepart or dieparts which surroundthis orifice. If further a similar rotation at the exit is allowable,any use of sealed revolving connections between conduits carrying theplastic material can therefore be avoided. However, in most cases arotation of a die exit for the described kind of structures is evenpreferable. Thus a tubular film, as known is often hauled of from thecircular die under a relative rotation between the die and the take-upmeans. Further, when producing an array of filaments, a twist will oftenbe advantageous. Consequently, it will usually be preferable to maintainthe rotation or rotations from inlet to outlet of the die, as shown ineach of the drawings. However, it is also within the scope of theinvention to keep the exit part fixed and therefore use one or severalrevolving and sealed joins between different parts of the die.

Depending e.g. on the flow-properties of the extruded material,different steps can be preferable to set-up the driving shear force atthe inlet orifice, e.g.:

(a) a rolling or scraping action against the inlet slot, cf. FIG. 1.

(b) by forming at least the inlet orifice of the conduit system from twoparts which are rotated relative to each other (at the same time asthere is produced an overall rotation of the material in one direction)and supplying the surface of at least one of said rotating parts inengagement with the material with a corrugations (vanes) adapted to thepumping action (directed obliguely with respect to the tangency)--cf.FIG. 3.

(c) similar to point (b) but with use of the well-known effect that aviscoelastic material under rotational shear between disks drag towardsthe axis of the disks due to the elastic forces created by the shear. Inthis case the corrogations (vanes) of point (b) are unnecessary, but itis a must that the passageway leads generally inwardly in the zone undershear and that the material used is visco-elastic.--cf. FIG. 4.

(d) by an insert (e.g. ringformed) in the inlet orifice relative towhich one or both surfaces of the inlet orifice rotate, cf. FIG. 5. Theinsert and/or orifice surface(s) can be supplied with corrugations(vanes) in analogy with point (b) above or there can be made use of theeffect described in point (c) above.

When extruding tubular items and using relative rotations as describedunder points (b) or (c) it is generally preferable to form the whole dieof two parts moving relative to each other from inlet to exit of theconduit. In these embodiments the construction of the die isparticularly simple.

It is of course necessary to adjust to each other, on one hand thevelocity by which the material is fed to the die (normally from aconventional extruder) and on the other hand the velocity of therotation or rotations which cause the pumping of material through thedie. Within limits however, there is a selfcontrolling effect in themeans described above under (a)-(d) Thus--to take (b) as an example--themore the inlet orifice is filled with material, the greater will be theportion of the corrugations (vanes) which are covered with material andwhich therefore participate in the pumping action.

As mentioned in the introduction the present invention has particularadvantages in connection with coextrusion of different materials. If thelatter exhibit very different flow properties, or e.g. if it isnecessary to extrude a more viscous material near the surfaces and aless viscous material in the core of a tubular item, then it may benecessary to use a die with two or more conduit systems, either with acommon exit orifice as shown in FIG. 1, or with separate exit orificesas shown in FIG. 2.

However, a preferable embodiment is characterized in feeding at leasttwo different coextrudable materials to one inlet orifice as distinctstrands and maintaining a generally laminar flow through the die. Saidstrands may with advantage have been joined to one composite strandbefore the feeding into the inlet orifice.

In order to utilize this embodiment for the formation of a laminate inthe usual sence, at least one strand of one of the materials isdistributed and merged into one layer in the inlet orifice, and at leastone stream of a different material is helically distributed and mergedto another layer, said layers being generally continous both in thecircumferential and the longitudinal direction of the extrusion. It willbe understand that this method--which is shown in FIG. 4--enables asimple coextrusion of many layers in a compact extrusion device.

In a further development of this method to produce a true laminate,different materials forming adjacent layers are fed in alternaterelationship at the boundaries between the layers to form ribformed,mutually interspersed extensions of each layer in said boundaries. (Seeagain FIG. 4, where the pattern at the feeding pipe (29) shows theinterspersing). There is hereby provided on improved bonding bymechanical means.

The present invention also relates to the device for carrying out themethods described in the foregoing. This is an extrusion die comprisinga circular inlet orifice, a circular exit orifice or a circular array ofexit orifices, generally coaxial with the inlet orifice, a generallyannular conduit or circular array of conduits also generally coaxialwith the inlet orifice, and connecting said inlet and said outlet, meansto feed at least one strand of material in plastic state into said inletorifice, means to rotate this orifice on the whole means at the inletorifice to produce a driving force towards the exit, and means tohaul-off the extruded material from the exit.

In a preferable embodiment of the device, both sides of the inletorifice are adjacent to a convex circular surface of the die. This isparticularly practical, since the elastic forces by the winding of thestrand around the device then helps to place the strand property in theorifice (provided the strand consists of visco-elastic material).

Another prefered embodiment of the device according to the invention ischaracterized in that the whole conduit system from the inlet orifice toand including the exit orifice forms an annular passageway without anyconnecting links passing from wall to wall through said passageway.Die-lines in the extruded tubular item is hereby avoided, with a higherstrength resulting.

BRIEF SUMMARY OF THE DRAWINGS

The invention will now be explained in further detail with reference tothe drawings 1-5, which schematically show 5 different embodiment of theextrusion device in perspective view with partial sections.

FIGS. 1, 3, 4 and 5 illustrate 4 different pumping means for thetransport of plastic material through the die while 1, 2 and 4 furtherillustrate 3 different ways of joining different materials to acoextrudate. It is to be understood that each of the 4 pumping means canbe combined with each of the 3 ways of coextruding.

For the sake of clarity all heating means have been omitted, whilebearings and driving means are shown only in FIG. 5.

DESCRIPTION OF THE DRAWINGS

In FIG. 1 the two extruder exits (1) and (2) feed two streams (in theabove called "strands") of molten polymer material (3) respectively (4)into circumferencial grooves or channels (5) and (6) forming the inletorifices of a co-extrusion die (7). Several sets of rollers (8) run inthe grooves and are provided with adjusting means (not shown). Spacers(not shown) are placed in the rear end of the channels (9) and (10)through which the two polymer streams are led. The streams are unitedimmediately before the exit orifice (11). Then the film (12) is blownand cooled in known manner and taken-up e.g. through nip-rollers (notshown).

The extrusion die itself can conveniently be heated by induction and itstemperature controlled by pyrometers, while the rollers (8) can beheated by means of a cyclotherm.

The rollers (8) can be substituted by scrapers (also heated). Further itis easy to visualize that the circular exit orifice of the die can besubstituted by a circular row of orifices by which there is formed anarray of bi-stranded filaments, which array is twisted to a twisted yarndue to the rotation of the die.

In FIG. 2 two extruder exits (11) and (12) feed polymer streams (13)respectively (14) into circumferential grooves (15) and (16) in anextruder-die (17). Rollers or other guiding and/or adjusting devices arenot shown but are preferably applied. Spacers (not shown) must be placedin the grooves (15) and (16) that go inwardly and end in partedcircumferential exit slots (18) and (19). The two polymer streams aredrawn, as indicated as an example, by nip-rollers (20) through guidingplates (21) over a cooled ring (22), and simultaneously laminated to afilm (23) that is cooled (not shown). Heating is carried out asexplained above.

While it is expected that the rolling or scraping action described inconnection with FIG. 1 is especially efficient in connection withmaterial of particularly low fluidity, e.g. very high molecular weightpolymers, the device of FIG. 3 is prefered in many other cases due toits simplicity. The die consists of two unconnected parts (24) and (25)which define a conduit consisting of the inlet orifice (26) and indirect connection herewith the exit oridice (27). (There may howeverconveniently be a longer passageway between the inlet and exitcomprising one or several widened chambers for further improvement ofthe distribution). The two parts (24) and (25) are held in position andin the proper distance from each other through external bearings and aredriven at different velocities through gear wheels (for detailsregarding the arrangement of bearings and gear wheels: see FIG. 5). Thedifferent velocities are indicated by the two arrows of differentlength. In order to achieve an efficient pumping action, the walls ofthe inlet orifice (26) are supplied with suitable vanes (28) which hereare only shown on one of the parts.

By similar means as shown in FIGS. 1 and 2 (but not shown here) a stream(strand) of molten polymer is fed into the inlet orifice (26) and atubular film is taken off from the exit orifice (27). Also in thisembodiment the heating of the die can be by induction, but due to thesimplicity and compactness of the construction it is even possible touse open flames.

At the same time as the two parts (24) and (25) move relative to eachother, it is essential that the material fed into the die is rotated onthe whole in order to become properly distributed. The arrows indicatethat they rotate at different velocities in the same direction. It isalso allowable to let one stand still, or even to rotate the two partsin opposite directions however, with different nummerical velocities sothat the material on the average is always rotated in one direction.

In FIG. 4 the rotating extrusion device is the same as in FIG. 3 exceptthat the vanes 28 are omitted. As known from conventionaldisk-extruders, a differential velocity of the two parts (24) and (25)will produce a pumping effect in visco-elastic material due to the factthat the shear-stresses have a component directed inwardly.

FIG. 4 further illustrates a very practical and efficient way ofproducing a laminate, in this case with 3 plies. 3 different materialsfrom 3 different extruders (not shown) are joined and extruded from acommon die (29) as a composite strand (rod or filament) consisting ofthe 3 sub-strands (plies) (30) (31) and (32). Due to the rotation of thetwo die parts (24) and (25) the composite strand is spirally wound-up inthe orifice (26) with the ply (30) adjacent to part (24) and (31) in themiddle. By the spiral winding-up and the continuous forewarding of thematerial, each of the sub-strands (30) (31) and (32) will thereby mergewith itself to a tubular ply. Instead of using only one coextrusion die(29) it can be advantageous to use two or more similar dies extrudingthe 3 materials in the same succession and mutually adjusted so thatthere are formed 3 merged plies of multi-spiral configuration.

A special feature of the coextrusion die (29) is means to formcorrugated boundaries (33) and (34) between the 3 sub-strands, or inother words to intersperse the components with each other at theirboundaries. This is obtained when the die-plates which separate the 3streams of material have a zig-zagging cross section as shown. However,the corrogated die-plates need not extend to the exit of the die (29)but can be located far backward in this die e.g. before this isnecked-in at (35).

The composite strand consisting of the plies (30), (31) and (32) ispreferably substantially drawn-down in the free space between the exitof (29) and the orifice (26). The dimensions of the corrogations at theboundaries of the plies will hereby be reduced, and it will be easy toget them down to a microscale, e.g. between 1 and 100 microns. In thefinal product these regular corrugations will essentially improve thebonding between the plies in cases when the adhesive bond as such ispoor.

In case the adhesive bond as such is satisfactory, there will not be anyneed to intersperse the plies at their boundaries.

The drawing only shows 3 plies, but it is a relatively simple matter tocoextrude even a great number of plies side-by-side in the die (29)--,particularly when the plies are joined to one stream before thenecking--in at (35).

The joining of the different materials to one composite strand beforethey are fed into the inlet orifice (26) is not indispensable but willusually be preferable in order to achieve the most precise merging ofeach of the plies to one tubular layer.

It is not necessary to use plain surfaces of the conduits of parts (24)and (25). There may be driving corrogations (vanes) but relatively lowor shallow. The driving system of rollers or scrapers, cf. FIG. 1, isalso applicable but in any case a generally laminar flow must be securedto produce and maintain the layers.

In special cases there can be advantages in producing a blendedstructure in which the components are interspersed with one another allover or in which one is dispersed in another.

In FIG. 3 and 4 the dielips at the exit (27) rotate relative to eachother. The shear at the exit can introduce tensions which can make thecontrol of the extruded film "bubble" difficult if the rheologicalproperties of the material or materials are unfavourable.

The embodiment shown in FIG. 5, takes care of this difficulty since itallows the two parts (24) and (25) to rotate at the same velocity (andin the same direction).

This is achieved by means of a ringformed insert fixed through severalsupports of which one (36) is shown. There is hereby established adriving shear between the insert (35) and each of the parts (24) and(25). The insert is shown supplied with vanes (37).

There can also, or alternatively, be vanes on the inlet orifice surfacesof (24) and (25) or all vanes (corrogations) can be omitted. There arepreferably fed one or several strands of material on each side of theinsert (35).

This drawing further shows the bearings (38) and gear-wheels (39) foreach of the dieparts (24) and (25).

Further improvements can be achieved if the insert (35) is made rotable,e.g. through teeth and bearings at its outer circumference. A highdistributing and pumping effect can thereby be obtained through fastrotation of the insert, while the rotation of (24) and (25) can be slowto facilitate the take-off of the tube. Its is even possible to makeparts (24) and (25) fixed, by which the construction is facilitated.However, the distribution will generally hereby be much less even.

In each of the drawings the extrusion through the circular die takesplace inwardly from the outer circumference. This facilitates thefeeding when the material(s) are viscoelastic. However, with suitablefeeding means such as rollers or scrapers, the feeding can also takeplace into an inlet orifice at one of the ends of the cylindrical ordisk-formed dieparts, or even from the inner circumference.

Further there has been shown a free space between the feeding extrusiondevice and the rotating material in the inlet orifice. This is alsogenerally advantageous especially when the material is viscoelastic, butis no necessity.

The drawings have been described particularly in connection withextrusion of molten thermoplastic polymer material for tubular items(e.g. sheeting). However, with suitable feeding and take-up means itwill also be advantageous for extrusion of other materials in plasticstate. Thus, as an example, one or several polymer solutions can beextruded form to a twisted yarn of filaments through a circulararrangement of orifices. The filaments can be solidified by drying or ina coagulation bath. Depending on the arrangement, there can be extrudedmono- or multilayered filaments and/or filaments of differentcomposition.

As a second example of special uses, the invention can be used forextrusion of pipes from inorganic fibres held together by curableprepolymers or the like. The pumping means in direct connection with theshaping of the pipe is very advantageous in such highly thixotropicmaterials.

As a third example the invention will be suitable in connection withextrusion of glas, e.g. coextrusion of differently coloured glas toobtain special effects, or extrusion of glas with metal fibres or otherhigher melting fibres as reinforcement.

As a fourth example the invention will be suitable in connection withextrusion of socalled plastic metal.

As a fifth example the invention will be suitable in connection withextrusion of clay, cement and the like e.g. reinforced with fibres.

As a sixth example the invention will be suitable in connection withextrusion of bread-like foodstuff, e.g. for coextrusion of viscous sugarsolution and dough which is subsequently baked.

As a seventh example the invention will be suitable for the extrusion ofmeat-like structures, from highly viscous, dissolved or swollen protein,e.g. coextruded with a viscous sugar solution, caramel and/or dough. Thecoextrudate is subsequently solidified.

What I claim is:
 1. An apparatus for extruding a continuous ordiscontinuous tubular sheet of an extrudable plastic material whichcomprises (a) a rotatable extrusion die having on its exterior at leastone generally continuous circular inlet channel, a continuous ordiscontinuous annular extrusion orifice at one end of said die spacedfrom and coaxial with said channel, and a continuous or discontinuousannular passage inside said die communicating between the bottom of eachsuch channel and said orifice; (b) means for rotating said die andchannel about its axis; (c) means for delivering to at least one pointon the path of said channel at least one pressure free flowable streamof said extrudable material to lay a ribbon of material within saidchannel; (d) means associated with said channel and operative uponrotation of said die to apply pressure against the material laid in saidchannel downstream of the point of delivery to advance the materialthrough the communicating passage and out of said die orifice; and (e)means for collecting the thus extruded film.
 2. An extrusion apparatusaccording to claim 1 in which the inlet channel extends peripherallyaround the die exterior.
 3. An extrusion apparatus according to claim 1in which the inlet channel, passageway and exit orifice form acontinuous annular passageway passing from one end of the die to theother.
 4. The extrusion apparatus of claim 1 wherein the opposite sidesof said channel are constituted by separate rotatable parts of said dieand including means for rotating said separate parts relative to oneanother during rotation of said die.
 5. The extrusion apparatus of claim4 wherein at least a portion of said communicating passage adjacent saidchannel is defined by said separate relatively rotating die parts. 6.The extrusion apparatus of claim 1 comprising vane means within saidchannel for advancing the material laid within said channel into saidcommunicating passage.
 7. The extrusion apparatus of claim 6 whereinsaid vane means continuously advances said material during rotation ofsaid die.
 8. The extrusion apparatus of claim 4 wherein vane means arecarries on at least one side of said channel for advancing said materialinto said communicating passage.
 9. The extrusion apparatus of claim 6wherein said vane means are supported for independent movement relativeto said channel.
 10. An extrusion apparatus as in claim 1 wherein saiddelivering means delivers a composite stream of layers of multipleextrudable materials and includes means for creating a corrugatedboundary between the adjacent layers in said stream.